Pull guides are known in various embodiments, which guides pull each sheet, mainly by static friction, against a fixed stop, the actual side mark. After arriving at the side mark, the sheet can immediately come to rest, because the pulling mechanism, which is only in slight contact with it, continues to pull on the sheet. However, the static friction immediately is switched to sliding friction.
Driven pulling rails, pulling rollers or pulling segments are used in a sheet-feeding table. If the sheet has arrived at the front marks, it is first pushed from above on the driven portion of the pulling device underneath the sheet by the use of a roller, which can be precisely adjusted, which roller is spring-loaded and which is cyclically moved up and down. The length of the pull of the pull guide is always slightly greater than the scatter width of the incoming scaled layers of sheets, plus a minimum pulling length of a few millimeters, up to the fixed side mark stop. The latter is adjustably fastened on the sheet-feeding table or on the comb plate, depending on the sheet format and the desired lateral position of the sheets running into the printing press.
These known pull guides have the disadvantage that they clamp the sheet from above and below in the course of pulling it. For this reason, the pull guide must remain open at the end of the pulling operation until each sheet end has passed the pull guide line, i.e. until each sheet end has cleared it. Only then can the successive sheet, which is already located in the front marks, be pulled by the pull guide. The third sheet of the incoming stream of scaled sheets must be sufficiently remote from the front marks and the pull guide line so that it has not yet reached the clamping pull guide working on the second sheet, i.e. is closed.
For rapidly running sheet printing presses, it is customary to keep the plate cylinder and the rubber blanket cylinder as small as possible. In that case, the paper running times are shorter, and the manufacturing expenses are less. The sheet length often can be ¾ to ⅚ of the plate cylinder circumference, so that the cylinder grooves are short and the sheets follow each other very closely. Clamping pull guides can no longer function, because the long sheets clear the pull guide lines too late for the clamping pull guides to pull the next sheet. In these cases, suction pull guides are used, in which suction pull guides the pressure roller extending down from above, is omitted.
A driven suction pull guide strip is located in the feed table and pulls each sheet in by the provision of a sufficient number of small suction air holes, and pulls each sheet transversely, in relation to the running direction of the sheets, against a fixed side mark. In this case, the suction air is adjusted so finely, for each paper thickness up to cardboard, that each sheet is pulled by the suction orifice against the side mark by the use of static friction and is deposited there, while the sliding friction, which now starts automatically, allows the further movement of the suction strip up to dead center.
Thus, known suction pull guides only act on the sheet from below without any clamping effects. They make possible an operation in the covered state of the preceding sheet end, and therefore accomplish greater sheet output per hour than prior clamping pull guides. However, it is disadvantageous that the third successive sheet, which is moved in underneath the sheet to be aligned in the scaled flow, must not reach the working pull guide, the same as with clamping pull guides, because it cannot get through between the second sheet that is grasped by suction, and the suction orifice. It can only do so if the suction pull guide does not operate, i.e. if the suction pull guide is “open” for sheets moving up from below.
The disadvantages of the generally known clamping and suction pull guides for the lateral alignment of sheets could be avoided if a lateral pulling device operating from above were provided.
DE 33 05 219 C2 describes the employment of a suction pull guide for very short scale distances, which suction pull guide is operating from above.
A device for the lateral alignment of sheets is known from DE 100 55 564 A1. An effective suction surface is greater in the conveying direction of the sheets than in the transverse direction.
DE 33 02 873 C2 discloses a suction gripper acting from above, which suction gripper is lifted for further conveying a successive sheet underneath the sheet which is just to be aligned.
DE 11 10 656 B shows a back-and-forth pivotable suction segment for the lateral alignment of sheets.
U.S. Pat. No. 2,167,823 discloses a device for aligning sheets transversely with respect to the sheet running direction. A holding device for transporting a sheet is arranged to move the sheet against a side mark, and at least two sheets are arranged on top of each other in a scaled manner in the sheet running direction. An effective holding surface extends in the sheet running direction, which surface is longer in the longitudinal direction than in the transverse direction, and wherein the holding device is arranged for acting from above on the sheet. In this case, three sheets are simultaneously arranged in the area of the holding device.
DE 2735 711 A1 shows a device for the lateral alignment of sheets by the use of a suction strip acting from below.
DE 27 11 554 A1 and DE 653 308 C each describe a device for aligning sheets. An end of an already aligned sheet trailing in the sheet running direction is again moved away from a side mark transversely to the sheet running direction.
DE 198 22 307 A1 discloses a device for aligning sheets transversely in respect to the sheet running direction. A transport roller, which transport the sheet from underneath, moves the sheet against a side mark and perform 1/N revolutions per sheet to be aligned.
A device for the lateral alignment of sheets by the use of circulating suction rollers acting from above is known from U.S. Pat. No. 1,728,329.